1. Field of the Invention
The present invention relates to a lens barrel which can be used as a photographing lens barrel of a camera.
2. Description of the Related Art
A conventional lens barrel in which each of linearly guided front and rear lens groups is provided with a set of follower pins which are respectively engaged in a corresponding set of cam grooves (cam slots) formed on a rotating cam ring so that the linearly guided front and rear lens groups move in an optical axis direction without rotating about the optical axis by rotation of the cam ring to move each of the front and rear lens groups between an accommodation position and a ready-to-photograph position in front of the accommodation is known in the art.
However, if the diameter of the cam ring is small, a reduction of the pitch of each cam groove (i.e., a reduction of the angle of inclination of each cam groove relative to a circumferential direction of the cam ring) causes the set of cam grooves for the first lens group and the set of cam grooves for the second lens group to interfere with each other, or causes the front and rear lens groups positioned at their respective accommodation positions to interfere with each other, to thereby get stuck (jam) thereat even if the cam ring is rotated to move the first and second lens groups forward from their respective accommodation positions.
Among such type of lens barrels, in a lens barrel required to be designed compact as much as possible, it is sometimes desirable not to rotate the cam ring for the purpose of preventing the cam ring from interfering, with any peripheral elements while moving the cam ring in the optical axis direction in a predetermined moving section of the cam ring from a fully retracted position thereof.
Moreover, in the above described conventional type of lens barrels, backlash occurs between the cam ring and a guiding mechanism for guiding the cam ring in the optical axis direction when the cam ring is moved to a ready-to-photograph position thereof. Such backlash deteriorates the performance of the focusing system.
The present invention provides a lens barrel having front and rear lens groups and a cam ring on which cam grooves for driving the front and rear lens groups are formed, wherein front and rear lens groups can be driven to move forward smoothly from their respective accommodation positions in an optical axis direction by rotation of the cam ring even if the angle of inclination of each cam groove formed thereon with respect to a circumferential direction of the cam ring is small.
The present invention provides a lens barrel in which the cam ring is prevented from interfering with any peripheral elements while moving in the optical axis direction in a predetermined moving section of the cam ring from a fully retracted position thereof.
The present invention provides a lens barrel in which backlash is prevented from occurring between the cam ring and a guiding mechanism for guiding the cam ring in the optical axis direction with a simple mechanism.
For example, in an embodiment, a lens barrel is provided, including a front lens frame which supports a front lens group and includes a first cam follower, the front lens frame being guided linearly in an optical axis direction without rotating about the optical axis; a rear lens frame which supports a rear lens group and includes a second cam follower; a cam ring driven to rotate about the optical axis, the cam ring including a first cam groove and a second cam groove in which the first cam follower and the second cam follower are respectively engaged; the first cam groove including a first moving section for moving the front lens frame in the optical axis direction, and a first accommodation section for moving the front lens frame behind a position of the front lens frame of which the first follower is engaged in the first moving section; the second cam groove including a second moving section for moving the rear lens frame in the optical axis direction, and a second accommodation section for moving the rear lens frame behind a position of the rear lens frame of which the second follower is engaged in the second moving section, the second accommodation section including an accommodation position at which the rear lens frame is positioned rearmost; and a guiding mechanism, provided between the front lens frame and the rear lens frame, for allowing the rear lens frame to rotate about the optical axis relative to the front lens frame when the second cam follower is engaged in a vicinity of the accommodation position of the second accommodation section, and for prohibiting the rear lens frame from rotating about the optical axis relative to the front lens frame while allowing the rear lens frame to move only in the optical axis direction relative to the front lens frame when the second cam follower is engaged in a section of the second cam groove which includes the second moving section and excludes the vicinity of the accommodation position.
The lens barrel can further include a shutter unit fixed to the rear lens frame; and a flexible PWB which extends rearward from the shutter unit so that a drive signal can be transmitted to the shutter unit via the flexible PWB.
The lens barrel can further include an elastic band, which is engaged with the flexible PWB to pull a portion of the flexible PWB in a direction away from the optical axis.
The elastic band can be a rubber band.
The multi-direction guiding mechanism can include a linear guide groove formed on an inner peripheral surface of the front lens frame to extend parallel to the optical axis; a rotation-permitting groove, formed at a front end of the linear guide groove, which communicatively connects with the linear guide groove, a width of the rotation-permitting groove being greater than a width of the linear guide groove in a circumferential direction of the front lens frame; and a linear guide projection, formed on the rear lens frame, which is engaged in the rotation-permitting groove when the second cam follower is engaged in the vicinity of the accommodation position, and which is engaged in the linear guide groove when the second cam follower is engaged in the section of the second cam groove which includes the second moving section and excludes the vicinity of the accommodation position.
The front lens frame can include an inner flange for supporting the front lens group, a circumferential opening being formed on the front lens frame. The rear lens frame can include a front projecting portion, on which the linear guide projection is formed, the front projecting portion projecting forward to extend through the inner flange through the circumferential opening when the second cam follower is engaged in the vicinity of the accommodation position.
The inner flange can be formed on the front lens frame at a front end thereof.
The lens barrel can be a zoom lens barrel, wherein the first moving section and the second moving section constitute a first zooming section and a second zooming section for moving the front lens group and the rear lens group to perform a zooming operation, respectively.
The rear lens frame can rotate about the optical axis via rotation of the cam ring when the second cam follower is engaged in the vicinity of the accommodation position.
In another embodiment, a lens barrel is provided, including a front lens frame which supports a front lens group and includes a first cam follower, the front lens frame being guided linearly in an optical axis direction without rotating about the optical axis; a rear lens frame which supports a rear lens group and includes a second cam follower; a cam ring driven to rotate about the optical axis, the cam ring including a continuous cam groove in which the first cam follower and the second cam follower are engaged; wherein the continuous cam groove includes a first moving section for moving the front lens group in the optical axis direction; a first accommodation section for moving the front lens frame behind a position of the front lens frame of which the first follower is engaged in the first moving section; a second moving section for moving the rear lens group in the optical axis direction; and a second accommodation section for moving the rear lens frame behind a position of the rear lens frame of which the second follower is engaged in the second moving section, the second accommodation position including an accommodation position at which the rear lens frame is positioned rearmost, in that order from one end of the continuous cam groove; and a guiding mechanism for allowing the rear lens frame to rotate about the optical axis relative to the front lens frame when the second cam follower is engaged in a vicinity of the accommodation position of the second accommodation section, and for prohibiting the rear lens frame from rotating about the optical axis relative to the front lens frame while allowing the rear lens frame to move only in the optical axis direction relative to the front lens frame when the second cam follower is engaged in a section of the second cam groove which includes the second moving section and excludes the vicinity of the accommodation position. The second accommodation section is formed to firstly make the rear lens frame move in the optical axis direction while making the rear lens frame rotate about the optical axis relative to the front lens frame via the second cam follower engaged in the second accommodation section, and to subsequently make the front lens frame guide the rear lens frame in the optical axis direction without making the rear lens frame rotate about the optical axis when the first cam follower of the front lens frame moves from the first accommodation section to the second moving section by rotation of the cam ring.
The lens barrel can be a zoom lens barrel, wherein the first moving section and the second moving section constitute a first zooming section and a second zooming section for moving the front lens group and the rear lens group to perform a zooming operation, respectively.
The guiding mechanism can include a guiding portion formed on the front lens frame, wherein the front lens frame firstly comes into contact with the rear lens frame and subsequently presses the rear lens frame to move the rear lens frame forward in the optical axis direction when the first cam follower passes the second moving section while moving from the first accommodation section toward the first moving section; and an engaging portion formed on the rear lens frame, the engaging portion being engaged with the guiding portion to be guided linearly in the optical axis direction by the guiding portion, wherein a side edge of the second accommodation section firstly comes into contact with the second cam follower, and subsequently the side edge presses the second cam follower to rotate the rear lens frame about the optical axis so that the engaging portion enters the guiding portion when the rear lens frame is moved forward by the front lens frame.
In another embodiment, a lens barrel is provided, having an optical system having a plurality of lens groups, the lens barrel including a lens supporting frame to which a frontmost lens group of the plurality of lens groups is fixed; a first moving frame to which the lens supporting frame is screw-engaged; a second moving frame to which a rear lens group of the plurality of lens groups which is positioned behind the frontmost lens group is supported; and a support frame movement mechanism for moving the first moving frame and the second moving frame between respective ready-to-photograph positions and respective accommodation positions located behind the respective ready-to-photograph positions in an optical axis direction. The support frame movement mechanism makes the first moving frame and the second moving frame rotate about the optical axis relative to each other with the lens supporting frame and the second moving frame being in contact with each other when the first moving frame and the second moving frame are respectively positioned in the vicinity of the respective accommodation positions. One of the lens supporting frame and the second moving frame includes a low-frictional portion provided on a contacting surface thereof.
The low-frictional portion can be a low-frictional sheet fixed to the contacting surface.
A fixing position of the lens supporting frame relative to the first moving frame in the optical axis direction can be adjusted via the screw-engagement therebetween during assembly.
The low-frictional sheet can be fixed to a contacting surface of the second moving frame which comes into sliding contact with a contacting surface of the lens supporting frame.
The lens barrel can be a zoom lens barrel.
In another embodiment, a lens barrel is provided, having at least one movable lens frame and a cam ring for moving the movable lens frame in a direction of an optical axis via a movement of the cam ring which is rotatable about the optical axis and movable in the optical axis direction, the lens barrel including a stationary ring provided around, and coaxial with, the cam ring; a rotatable ring provided around, and coaxial with, the stationary barrel, the rotatable ring being driven to rotate about the optical axis; a cam follower which extends radially outwards from the cam ring; and a cam through-slot and a rotation transfer groove which are formed on the stationary ring and the rotatable ring, respectively, so that the cam follower is engaged in the cam through-slot and corresponding the rotation transfer groove. The cam through-slot includes a linear slot portion which extends parallel to the optical axis; and an inclined slot portion which extends in a direction inclined to both the optical axis direction and a circumferential direction of the stationary ring. The rotation transfer groove includes an inclined groove portion in which the cam follower is engaged when the cam follower is engaged in the linear slot portion, and a linear groove portion in which the cam follower is engaged when the cam follower is engaged in the inclined slot portion.
The linear slot portion can be formed on the stationary barrel at a position to fully retract the cam ring.
The movable lens frame can include a front movable lens frame and a rear movable lens frame; the lens barrel further including a linear guide ring which guides the front movable lens frame linearly in the optical axis direction without rotating the front movable lens frame about the optical axis; and a biasing device provided between the linear guide ring and the front movable lens frame, for biasing the front movable lens frame rearwards. Each of the front movable lens frame and the rear movable lens frame moves to an accommodation position thereof via a biasing force of the biasing device when the cam follower of the cam ring moves along the linear slot portion toward an end thereof corresponding to an accommodation position of the cam ring.
The lens barrel can be a zoom lens barrel.
The biasing device can include at least one helical compression spring.
In another embodiment, a lens barrel is provided, in which a movable lens frame is driven in an optical axis direction via rotation of a cam ring, the lens barrel including a cam follower which extends radially outwards from the cam ring; a stationary barrel provided around, and coaxial with, the cam ring, the stationary barrel including a cam through-slot in which the cam follower is engaged, the cam through-slot including a lens-frame-driving slot portion for moving the movable lens frame in the optical axis direction in a predetermined operating range; and a biasing ring for biasing the cam ring toward the stationary ring in the optical axis direction. The biasing ring includes a contacting surface which comes into contact with a portion of the cam follower which projects radially outwards from the cam through-slot to press the portion of the cam follower against a side edge of the cam through-slot when the cam follower is engaged in the lens-frame-driving slot portion of the cam through-slot.
The biasing ring can include a projection, a rear end surface thereof constituting the contacting surface.
It is desirable for the cam through-slot to extends in a circumferential direction of the stationary barrel.
The lens barrel can further include a rotatable ring provided around, and coaxial with, the stationary barrel, the rotatable ring being driven to rotate about the optical axis. The rotatable ring includes a rotation transfer groove formed on an inner peripheral surface of the rotatable ring so that the cam follower is engaged in the cam through-slot and a corresponding the rotation transfer groove, the cam ring being rotated by rotation of the rotatable ring via engagement of the cam follower with the rotation transfer groove.
The lens barrel can further include a biasing device which biases the biasing ring and the rotatable ring to approach each other in the optical axis direction; wherein the biasing ring is mounted to the rotatable ring via the biasing device.
The lens barrel can further include a rotatable ring provided around, and coaxial with, the stationary barrel and driven to rotate about the optical axis, the rotatable ring including a rotation transfer groove formed on an inner peripheral surface of the rotatable ring so that the cam follower is engaged in the cam through-slot and a corresponding the rotation transfer groove, the cam ring being rotated by rotation of the rotatable ring via engagement of the cam follower with the rotation transfer groove; and a biasing device which biases the biasing ring and the rotatable ring to approach each other in the optical axis direction. The biasing ring is mounted to the rotatable ring via the biasing device. The projection is formed on the biasing ring to extend radially inwards to extend through the rotatable ring through a through hole formed on the rotatable ring immediately in front of the rotation transfer groove.
The lens barrel can be a zoom lens barrel, the lens-frame-driving slot portion constituting a zooming slot portion for moving the movable lens frame in the optical axis to perform a zooming operation.
The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 2001-83685, 2001-83686, 2001-83687, 2001-83688 and 2001-83689 (all filed on Mar. 22, 2001) which are expressly incorporated herein by reference in their entireties.